I just witnessed the hilarious gloriousness of the Radiant Story system.
My first quest from the Companions is "Hired Muscle", where you're supposed to intimidate x (where x is an npc picked at random from a compiled list, I guess).
The person I'm supposed to intimidate is... Faendal. Who's my follower at the moment. And he's standing right behind me when I get the quest.
So, me and Faendal return to Rivenwood. We then proceed to his front lawn, where we have a fist fight.
Afterwards I ask him to follow me again, which he happily obliges to do. No grudges. No offence.

I don't know if this was a bug or if the game just reeeally wanted my character to punch his inexplicably loyal friend in the face.